1. Field of the Invention
The present invention pertains generally to the leak-free passage of electrical conductors and conduits through radiation shielding. More specifically, the invention pertains to radiation-opaque pathways for electrical conductors in the shielding between the radiation source and the radiation detector in a well logging sonde.
2. Description of the Prior Art
In nuclear experiments, shielding material is used between the radiation source and the radiation detector to prevent neutrons and gamma rays from advancing directly into the detector from the source. In nuclear well logging sonde applications, shielding becomes critical due to the restricted space available within the well bore. A typical well logging sonde has a tubular housing approximately 6 meters long and 11 centimeters in diameter. The sonde carries both the source and the detector. The source-to-detector space available for shielding is between about 31 centimeters to about 69 centimeters, depending on the particular application. Consequently, in a practical application, adequate shielding to prevent all neutron or gamma ray leakage to the detector is prohibited. This problem of nuclear leakage is amplified in a typical sonde since the electrical conductors for power and control circuits must pass through the shielding material. Any straight hole in, or bypass of, the shielding material provides a path for radiation leakage, increasing the background radiation reaching the detector and thus reducing the accuracy of the data obtained. It is also the case that, even where the space for shielding is ample, drilling a long, small diameter hole, more than about sixty centimeters in length, through the shielding material to provide a passageway may be very difficult.